The present invention relates to an aircraft model-based sensor system, and more particularly to a model-based virtual sensor system for calculation of angular acceleration from measured dynamic quantities that are available in a flight control computer for subsequent utilization in feedback flight control systems to reduce aircraft flight loads while maintaining maneuvering performance.
The structure of a rotary-wing aircraft is designed to withstand flight loads that occur during all phases of aircraft operation such as aerodynamic forces and moments from the fuselage and the rotor system. Flight loads typically peak during maneuvering flight. An aircraft structural envelope is designed relative an aircraft Operational Flight Envelope (OFE) and Service Flight Envelope (SFE) with a margin to more than accommodate peak flight loads. The margin is often provided by reinforced aircraft structure. Although effective, aircraft weight is concomitantly increased.
Loads Aware Control Laws afford the opportunity to save structural weight by limiting the peak loads encountered during flight. Main rotor generated hub moments are the primary contributors to these peak loads as rotor hub moments are transferred to the aircraft structure through the rotor system. One way to reduce hub moments on a rotary-wing aircraft is to control rotor blade flapping without decreasing aircraft maneuverability and agility.
Control of rotor blade flapping requires accurate determination of moment for input into the Loads Aware Control Laws of a fly-by-wire flight control system. Determination through direct measurement of flapping or a related quantity requires a rotating frame measurement and a methodology to transfer that measurement to the fixed frame. Although direct measurement through a specially instrumented rotor hub having a sensor system within the rotating frame typical of flight test instrumented aircraft is conventionally utilized, such instrumentation may not be practical for operations in a field environment.
Accordingly, it is desirable to provide a model-based sensor system for use with a feedback flight control system to control rotor hub moment such that loads on the aircraft structure are reduced to thereby allow an aircraft structural envelope to more closely follow the aircraft OFE or SFE.